Power hammer



Nov.. 5, 1935.

c. B. COATES 2,020,018

POWER HAMMER Filed July 6, 1933 INVENTOR. Char/es B. Coafes ATTORNEY.

Patented Nov. 5, 1935 UNITED STATES PATENT OFFICE POWER HAIVHHER Application July s, 1933, Serial No. 679,161

9 Claims.

This invention relates to a percussive tool preferably, though not necessarily, operated by an electric motor as a prime mover and adapted to hammering purposes, such as tie tamping, chipping, drilling, riveting, or the like. More particularly the invention relatesto a hammer in which the motive power from the prime mover is utilized for the compression of air, which in turn operates upon a piston to impart blows to the tool.

.One of the. principal objects of the present invention is to improve hammers of the type described by increasing the speed of the piston and the force of blow. Another object is to reduce vibration. In accordance with these and other objects, the invention comprises a reciprocating cylinder'driven by an electric motor, and so constructed as to forma part of a variable volume "compression chamber in which air is alternately compressed "and rarefied. A hammer piston, disposed within the reciprocating cylinder, is propelled by compressed air admitted at the proper intervals through ports in the cylinder. These ports. are arranged to delay the movement of the "hammer piston until considerable compression has taken place in the compression chamber, ,Wherebythe full force of the compressed air is "applied to the hammer piston suddenly driving the piston forwardly at great speed to produce a heavy blow upon the tool. Afeature of the invention resides in means for exhausting the air ffrom; the inner cylinder, This means consists of ports in the cylinder and outer casing respecitiirelywhich are adapted to register in one position offth e cylinder. On the return stroke, the cylinder is lifted while the outer chamber sucks JairQfrom the interior of the cylinder causing 'thefharrimer piston to rise with the cylinder.

' f further object isv to prevent waste of lubricant ina' hammer having a chamber undergoing rapid-fluctuations of .air pressure. p In the present invention," this] is accomplished by making the reciprocating cylinder of two diameters, the larger diameter forming a part of g the compression chamber; and the small diameter being interposed between the compression chamber and the crank case.

other objects will appear more clearly from the description which follows. H

Referring to the drawing, Fig. 1' is a central ing'shown in its uppermost position; and ..Fig's;:2; 3 and 4 are sections of the barrel and contained parts showing the reciprocating cylinder and the piston in diiferent positions.

The construction illustrated inthe drawing comprises essentially the motor structure and its housing or casing at the upper or rearward end 5 of the tool, and a compression cylinder and a barrel connected therewith and containing the working parts, one of which is operated directly by the motor, the barrel also being adapted to receive the working tool at its lower or forward end. Referring'to Fig. 1, the motor, which is preferably an electric motor of the induction type, is provided with a casing or housing I!) inwhich are contained and supported the usual electric motor elements, such as the stator ll, rotor I2, and rotor shaft I3. A crankcase or gear case I4 is connected as by bolts IE to the motor housing [0. The upper end of the rotor shaft is supported in a bearing l6 within housing I0, while the lower end is mounted within a sleeve ll sup ported by the'bearing l8 within the crank case l4.- If desired, the sleeve I! may support a suitable fan 19 for cooling the motor.

A beveled pinion 2| is secured to or formed on the lower end of the rotor shaft l3. This pinion meshes with a bevelled gear 22 which is bolted to a flange 23 formed on a built-up crank. The crank is rotatably mounted in ball bearings '25 and 26, one of'the bearings being carried by a wall of the crank case 1.4 and the other by a closure 21 for the crank case. The crank comprises the journals 28 mounted in the aforementioned bearings, the flange 23, the-crank pin 29,'which is integral with flange'23, and a counterbalance 30 bolted to the crank pin- It will be understood that the'rotation' of the'rotor shaft l3 causesthe revolution of the crank about the axis 28, and the gear ratio is such as to cause 'the'crank to revolve at a much slower speed than the motor shaft.

A compression cylinder 32 is bolted to the crank case I4 at the lower end of the latter. Operating in this compression cylinder is a compound piston 33, 34, which is given a reciprocating motion through the medium of the crank pin 23, the ball hearing 35, the connecting rod 36 and the wrist pin 31 located in the end of the piston 33, 34.

The smaller diameter of the piston 33 operates in a close bore of the cylinder 32 and is packed by the piston rings 39. The larger diameter of 5 the piston 34 operates in at close bore and is packed'by the piston rings 40. The piston 33, 34 is provided with an internal cylindrical bore vatsitslower end to receive the striking piston, or hammer piston 42.

The bore 41 forms the inside diameter of a sleeve or cylinder 43, which is a part or continuation of the piston 33, 34 and which reciprocates, with a close fit, within the barrel 45. The piston 34 is provided with one or more leak ports 41 leading from the bore 4| to the compression chamber 50 within the compression cylinder 32. Sleeve 43 is provided with pressure ports 48 and exhaust ports 49. The compression cylinder is provided with breather ports and intake ports 52.

The object of the smaller diameter 33 with rings 39 of the compression piston, is to prevent the oil from leaking out of the crank case l4 too rapidly. A smaller amount, suflicient to lubricate the large diameter 34 of the piston 33, 34 and the striking piston 42 through ports 41 and 48, is accomplished by leaving a slight opening between the ends of each piston ring 39.

Bolted to the compression cylinder 32 is a compression head 54 and barrel 45. The compression head carries internal packing rings 55 for packing the cylindrical extension 43' of the piston. The barrel 45 is provided with exhaust ports 56, breather ports 51 and a tool bushing 58, preferably with a hexagonal or square hole in it to receive the shank of the tamper bar or other tool 59. Attached to the barrel 45 by means of bolts or otherwise is a tool retainer 60 which may be made with a split collar 8|, a rubber bumper 62 and a split bushing 63.

In operation, the rotation of the motor causes the reciprocation of the connecting rod 36, and of the pistons '33, 34, 42 in a manner obvious to those skilled in the art. The reciprocations of piston head 34 are efiective to produce alternate compression and rarefication of the air in compression chamber 50 for imparting power to the hammer piston 42 as will be described presently.

Fig. 1 shows the crank and consequently the pistons 33, 34, 42 at the upper end of the stroke,

the compression chamber 50 being, of course, at its maximum size and vented through intake port 52. The hammer piston 42 projects within the confines of piston head 34. As the piston 34 starts on the downward stroke, the air in the compression chamber is out 01f from port 52 and begins to be compressed. During the compression of this air, a small amount of it flows through the restricted opening 41 to feed the striking piston 42 down gradually. By the time the striking piston uncovers the pressure port 48 in the reciprocating sleeve 43, the air in chamber 50 has been greatly compressed, and the full pressure from this chamber is admitted through the large ports 48, driving the hammer piston forward until it strikes the end of the tamper bar 59 with great force. Fig. 2 shows the parts in the position that they may occupy when the full force of the air is first admitted to the bore 4| behind the striking piston. The force of the air drives a hammer piston to the Fig. 3 position where it is shown as striking the tool. During the rapid motion of the piston from the Fig. 2 to the Fig. 3 position, the reciprocating cylinder 43 continues to move downwardly, but at a speed considerably less than that of the hammer piston. The continued downward movement of the piston 34. continues to decrease the size of the compression chamber 50, thereby maintain'mg the pressure behind the hammer piston up until the time that the blow is transmitted to the tool.

' As the hammer piston reaches its striking position, shown in Fig. 3, the exhaust ports 49 on the reciprocating cylinder 43 become aligned with the exhaust ports 56 in the barrel 45. As a resuit the air in the reciprocating cylinder 43 and in the compression chamber 50 is vented through the ports 48, 49 and 55. The upward movement of the reciprocating cylinder closes the exhaust port 49 and the enlargement of the compression chamber 53 sucks air from the inside of the re ciprocating cylinder through pressure port 48 thereby creating a partial vacuum at the upper end of the hammer piston. As the reciprocating cylinder moves upwardly from the Fig. 4 position, the hammer piston, which has been traveling at a faster rate than the reciprocating cylinder, due

to its smaller area, continues its upward movement, as a result of the momentum it has acquired, until checked by the air pressure it produces in the pocket or cushion space above the ports 48, when the parts again reach their Fig. 1 position. Port 41 is so small that there is very little leakage of air through it during the short interval that the striking piston 42 is entering the cushion pocket.

. It will be apparent that the operation of the restricted passages 41 and of the hammer piston 42 in delaying the uncovering of pressure ports 48, until the pressure of the air in compression chamber 50 has approximately reached its maximum value, results in a more rapid movement of the piston and a more powerful blow than otherwise obtainable. If the compressed air were connected to the hammer piston during the initial stages of compression, as in the case of prior devices, the expansion of the air into the space rearwardly of the hammer piston would materially limit the maximum degree of compression.

In the foregoing description, the use of such terms as upper, lower and downward, will be understood to be the proper description when the tool is held in the downward position as shown in the drawing. However, it is obvious that the tool is capable of working in any desired position, even an inverted position, inasmuch as the action of the hammer piston depends upon the fluctua- ,tions of air pressure in the compression chamber,

rather than upon gravity.

While the invention has been described with reference to one particular illustrative embodiment, it will be understood that various features of the invention are of general application and not limited to: any particular type of motor, transmission mechanism or actuated tool.

What is claimed is:

1. In a power hammer, the combination of a barrel, a power operated hollow cylinder slidably fitting therein, said cylinder being closed at one end only, a hammer piston of uniform diameter 55 reciprocable within said cylinder and. adapted to project beyond the other end thereof, an annular compression chamber surrounding a portion of the cylinder, a flange on the cylinder forming one of the walls of the chamber, and one or more 00 piston-controlled ports leading from the compression chamber to the inside of the cylinder.

2. A percussive tool comprising a movable cylinder, a piston reciprocable therein, a variable volume fluid chamber exterior to said cylinder and 66 having one wall movable with the cylinder, one or more ports in said cylinder connecting the chamber to the interior of the cylinder to actuate the piston, said ports being under control of the piston, and fluid pressure means for moving the 70 piston to a position to uncover said ports.

3. A percussive tool comprising a movable cylinder, a piston reciprocable therein, a variable volume fluid chamber exterior to said cylinder and having one wall movable with the cylinder, (6

one or more fluid pressure ports in'said cylinder connecting the chamber to the interior of the cylinder to actuate the piston, said ports being adapted to be uncovered by the piston, and means comprising a restricted passage through the cylinder for moving the piston to a position for uncovering said ports.

4. A percussive tool comprising a casing, a cylinder reciprccable therein, a compression chamber outside said cylinder, a piston within said cylinder, a plurality of axially spaced ports in said cylinder leading from the interior thereof to the compression chamber, one of said ports being restricted to cause the piston to move slowly to uncover another port, the latter being relatively unrestricted to cause rapid movement of the piston.

5. A percussive tool comprising a casing, a reciprocating cylinder therein, a piston in said cylinder, an expansible and contractible chamber exterior to said cylinder, means for connecting said chamber to the interior of the cylinder for driving the piston in both directions, and exhaust ports in the cylinder and casing respectively, said ports being adapted to register in one position of the cylinder for exhausting the interior thereof.

6. A pneumatic tool comprising a crank case and a compression cylinder secured together, a piston head in said cylinder and driven from a crank shaft in said crank case, and means for providing a restricted flow of lubricant from the crank 7 case to the cylinder, said means comprising a sec- 0nd piston head and cooperating cylinder interposed between the first piston head and the crank case, and means for venting the cylinder intermediate the two piston heads.

'7. A percussive tool comprising a cylinder, a piston reciprocable therein, a variable volume fluid chamber exterior to and surrounding said cylinder, one or more fluid pressure ports in said cylinder connecting the chamber to the interior of the cylinder to actuate the piston, said ports being adapted to be uncovered by the piston, and means for moving the piston slowly to a position to uncover said ports, whereby said ports are uncovered after pressure has been built up in said fluid chamber.

8. A percussive tool according to claim 7 in which the means for moving the piston slowly comprises a restricted fluid passage from the fluid chamber to the interior of the cylinder.

9. A percussive tool comprising a casing, a cylinder reciprocating therein, a compression chamber outside of said cylinder, the interior of the cylinder providing a piston chamber closed at one end, a piston reciprocating within said piston chamber, means movable with the cylinder for compressing fluid in said compression chamber, one or more ports in the cylinder for connecting the compression chamber at a point spaced from the closed end of the latter, said port or ports being adapted to be uncovered by the piston, and means for admitting pressure fluid in limited amounts to the piston chamber between said port, or ports, and the closed end of the piston chamber, whereby to move the piston to a position to uncover the port or ports.

CHARLES B. COATES. 

